Updated Wednesday, January 23, 2013 at 01:31 AM
MELBOURNE, Australia — Serena Williams is out of the Australian Open after losing 3-6, 7-5, 6-4 to 19-year-old Sloane Stephens in a quarterfinal matchup of Americans.
Williams, a winner of 15 major tennis singles titles, hurt her back while attempting to pull up short of the net during the eighth game of the second set. She called for a trainer after the ninth game with the score 5-4 and on serve.
Stephens won the second set when Williams, serving slower than usual, was broken. The third-seeded Williams also had her service broken in the final game of the match.
Williams' winning streak was snapped at 20 matches; it was her first loss since Aug. 17.
At 2-1 and on the way to a changeover in the third set, Williams smashed her racket angrily on the court then threw it toward the chairs on the side of the court.
Stephens, seeded 29th, was competing in her first quarterfinal at a Grand Slam tournament.
Stephens, who is from Los Angeles, will play defending champion Victoria Azarenka of Belarus in the semifinals. The top-seeded Azarenka beat Svetlana Kuznetsova of Russia 7-5, 6-1.
Stephens has said she used to display a photo of Williams in her room.
"This is so crazy. Oh my goodness," said Stephens, wiping away tears in a TV interview after the match. "I think I'll put a poster of myself (up) now."
Stephens gave herself a pep talk on the morning of the match.
"When I got up," she recalled, "I was like, 'Look, dude, like, you can do this.' Like, 'Go out and play and do your best.' "
Williams, 31, didn't blame her back problem for the loss.
"Everyone at this stage in the locker room has something wrong with them. It's no excuse," she said. "I went for this drop shot and it just locked up on me. I couldn't really rotate after that.
"It was a little painful, but it's OK."
Williams said she thought about quitting the match "for a nanosecond."
Azarenka, after dropping serve in a long fourth game that went to deuce 10 times, recovered to dominate the rest of the match against Kuznetsova, a two-time major winner who was floating dangerously in the draw with a No. 75 ranking as she recovers from a knee injury.
Meanwhile, two-time defending champion Novak Djokovic of Serbia is through to the semifinals after a 6-1, 4-6, 6-1, 6-4 victory over No. 5 Tomas Berdych of the Czech Republic.
No. 3 Andy Murray of Britain beat Jeremy Chardy of France 6-4, 6-1, 6-2.
ANDREW BROWNBILL / AP
Sloane Stephens, 19, hits a backhand during Tuesday's victory over fellow American Serena Williams.